The invention relates to gate valves, and in particular, to gate valves that have an expanded gate valve assembly positioned therein for reciprocal movement transversely of the flow passage.
Although structures that continuously urge together the gate element and segment of an expanding gate valve assembly have been used heretofore, persons have continually sought to develop and improve such structures. It is very important that the gate element and segment immediately reach their collapsed position upon the displacement of the gate valve assembly from its fully open or closed position, and that they remain collapsed at all times when the gate valve assembly is not in its fully open or closed position. If the gate element and segment do not collapse when they should, the gate valve assembly may bind upon the valve seats which can result in a high operating torque required to move the gate assembly between open and closed positions.
Thus, it is highly desirable to provide an improved expanding gate valve assembly wherein the gate element and segment immediately reach their collapsed position upon the displacement of the gate valve assembly from its fully open or closed position. It would also be highly desirable to provide an improved expanding gate valve assembly that maintains the gate element and segment in a collapsed position when the gate valve assembly is not in its fully open or closed position.
Heretofore expanding gate valve assemblies have utilized a spring anchored at the opposite ends thereof to the gate element and engaging a single centrally disposed lug on the segment to continuously urge the gate element and segment toward a fully collapsed condition. This continuous urging was done in two principal ways: first, by providing the necessary force to help collapse the gate element and segment when the gate valve assembly is initially displaced from either its fully open or closed positions; and second, by providing the necessary force to maintain the gate element and segment together once they have been collapsed. In the former, before successfully urging the gate element and segment into a collapsed position, the spring must overcome resistance associated with the collapse of the gate element and segment. The principal components of this resistance are the weight of the segment and the frictional resistance associated with the gate element and segment having to slide on each other.
In the above described arrangement, when the gate element and segment are expanded away from each other, the single lug is only slightly displaced in the direction of relative movement of the segment from a transverse axis passing through the apex of the gate element as is the direction of the spring force acting upon the single lug. The consequence of this is that the spring does not efficiently overcome the resistances associated with the collapse of the gate element and segment and stronger springs must be utilized than if the expanding gate valve assembly more efficiently utilized the spring.
Heretofore, expanding gate valve assemblies have also utilized a pair of springs anchored to the gate and in engagement with a pair of pins on the segment. See the U.S. Pat. No. 4,189,127 issued to Constantino on Feb. 19, 1980. However, in the arrangement shown in U.S. Pat. No. 4,189,127 opposing longitudinal forces are continuously exerted against one another. Thus, the collapse of the gate assembly from its expanded to collapsed positions is resisted by the spring remote from the end of the segment leading with respect to the travel of the segment relative to the gate. Due to the relatively slight movement of the gate relative to the segment, it would appear that the force exerted by the leading spring to continuously urge the gate and segment together is not that much greater than the force exerted by the remote spring to resist this continuous urging. Consequently, these springs constantly oppose one another so that the device of the U.S. Pat. No. 4,189,127 appears to provide a significant resistance to the immediate collapse of the gate and segment upon their displacement from an expanded position.
Thus, it is highly desirable to provide an improved expanding gate valve assembly that more efficiently utilizes the spring forces. It is also highly desirable to provide an improved expanding gate valve assembly that more easily overcomes the resistance associated with the collapse of the gate element and segment. It is also highly desirable to provide an improved expanding gate valve assembly wherein a weaker spring is utilized than in earlier single lug assemblies of similar size. It is also highly desirable to provide an improved expanding gate valve assembly that does not provide any significant inherent resistances to the collapse of the gate and segment from their expanded to their collapsed positions.